Copper or copper alloy are applied in conductive components of EE device such as terminals, for example, connectors of semiconductor device, or movable conductive piece of electromagnetic relays. Specifically, brass (Cu—Zn alloy) has been widely used in the prior arts based on the consideration of a balance between strength, workability, cost or the like. Where the copper alloy is used in terminals such as connectors, surface of a Cu—Zn substrate (raw plate) is plated with tin (Sn) in many case with a main purpose of enhancing reliability of connection with a conductive member of the mating part.
In a conductive component such as connectors of the above-described constitution formed by plating Sn on the surface of the Cu—Zn alloy substrate, the Cu—Zn based alloy of the substrate is sometimes added with Sn and is used in the form of Cu—Zn—Sn based alloy so as to improve recycling efficiency and to improve the strength of the alloy.
In general, the production process of conductive component of EE device such as a connector of a semiconductor includes rolling the raw material copper alloy to form a thin plate (strip) having a thickness of about 0.05 to 1.0 mm, obtaining a member of a predetermined shape by blanking (stamping), and bending at least a partial portion of the stamped member. In many cases, in the usage of the thus formed conductive component, electric connection with the mating conductive member is achieved by making the vicinity of the bent portion of the conductive component contact the mating conductive member, and the contacting sate with the mating conductive member is maintained by spring property of the bent portion. In the copper alloy used in the conductive components such as connectors, excellent conductivity is required so as to suppress heat generation due to resistance heating. In addition, high strength and excellent rollability and blanking quality are required since the alloy is rolled to a thin plate (strip) and is subjected to blanking. Further, in the case of a connector that is formed by bending a copper alloy such that the vicinity of the bent portion is used to maintain contact state with the mating member by spring property of the bent portion, excellent stress relaxation resistance (SR resistance) is required for the copper alloy member in addition to the requirements for excellent bendability such that the contact state with the mating member in the vicinity of the bent portion is maintained satisfactorily for a long time (or even in high temperature atmosphere). That is, in the case of a terminal such as a connector that utilizes spring property of a bent portion for maintaining contact state with the mating member, contact pressure with the mating member is not maintained sufficiently resulting in tendency to occur defective contact in the early stage where the copper alloy has inferior stress relaxation resistance and time dependent relaxation of residual strain occurs in the bent portion or the residual strain in the bent portion is relaxed under a high temperature environment.
For example, Patent literatures 1 to 3 describe conventional arts which have been proposed as a solution for improving SR resistance of Cu—Zn—Sn based ally used in conductive components such as connectors. Patent literature 4 proposes a solution for improving SR resistance of Cu—Zn—Sn based alloy for lead frame.
Patent literature 1 describes improvement of SR resistance by making the Cu—Zn—Sn based alloy contain Ni, and thereby generating Ni—P based compounds. Patent literature 1 also shows that addition of Fe also improves the SR resistance. In the proposal described in Patent literature 2, strength, elasticity, and heat resistance of the alloy are improved by adding Ni and Fe with P to Cu—Zn—Sn based alloy. Even though SR resistance is not directly described in Patent literature 2, it is considered that the improvement of strength, elasticity, and heat resistance means the improvement of SR resistance.
The inventors also confirmed that the addition of Ni, Fe, and P to the Cu—Zn—Sn based alloy as proposed in Patent literatures 1, 2 is effective in improvement of SR resistance of the alloy. However, the proposals of Patent literatures 1 and 2 merely consider individual amount of each of Ni, Fe, and P. As a result of Inventors' experiments and research, it was made clear that the SR resistance cannot be always improved securely and sufficiently only by the control of the individual contents of these elements.
On the other hand, the proposal of Patent literature 3 describes that the SR resistance is improved by adding Ni to Cu—Zn—Sn based alloy and controlling Ni/Sn ratio to be within a certain range. Patent literature 3 also describes that the addition of small amount of F is also effective in improvement of SR resistance.
Even though the control of Ni/Sn ratio described in Patent literature 3 is indeed effective in improvement of SR resistance, Patent literature 3 describes nothing about a relationship between the P compounds and the SR resistance. As described in Patent literatures 1 and 2, P compounds may have strong influence on the SR resistance. In the proposal of Patent literature 3, nothing is considered about the relationship between the SR resistance and contents of elements such as Fe and Ni that constitute P compounds. The experimental study by the inventors also made clear that sufficient and secure improvement of SR resistance could not be achieved only by a constitution in accordance with Patent literature 3.
Patent literature 4 related to a lead frame describes that improvement of SR resistance is enabled by adding Ni and Fe with P to Cu—Zn—Sn based alloy and simultaneously controlling atomic ratio of (Fe+Ni)/P to be within the range of 0.2 to 3, and thereby generating Fe—P based compounds, Ni—P based compounds, or Fe—Ni—P based compounds.
However, as a result of experimental study by the inventors, it was made clear that sufficient improvement of SR resistance cannot be obtained only by the control of the total amount of Fe, Ni, P and atomic ratio of (Fe+Ni)/P as described in Patent literature 4. Although exact reason is not clear, as a result of experiments and research by the inventors, it was made clear that control of Fe/Ni ratio and Sn/(Ni+Fe) ratio is important in addition to control of total amount of Fe, Ni, and P and (Fe+Ni)/P ratio and that SR resistance cannot be improves securely and sufficiently without controlling these content ratios with appropriate balance.
As explained above, in accordance with the conventional arts that have been proposed for improving SR resistance of Cu—Zn—Sn based copper alloy for conductive components of EE device, effect of improving SR resistance is not yet secure and sufficient, and further improvement is demanded. In the component such as a connector that has a bent portion formed by bending a thin plate of rolled copper alloy, and is use such that the vicinity of the bent portion is made contact with the mating member, and the contact state with the mating member is maintained by spring property of the bent portion, defective phenomena such as defective contact may tend to occur in the early stage if the contact pressure with the mating member is not maintained as a result of relaxation of residual strain over time or under high temperature environment. To avoid such a problem, large thickness of material has been required in the conventional arts, resulting in increase of raw material cost, and increase of weight of the component.